Polyester modified with polyethylene glycol and pentaerythritol

ABSTRACT

A polyester composition is disclosed that is particularly suitable for filament. The composition is formed of polyethylene terephthalate; polyethylene glycol in an amount sufficient to increase the wetting and wicking properties of a filament made from the composition to a level substantially similar to the wetting and wicking properties of cotton and other cellulosic fibers (natural or synthetic) but less than the amount that would reduce the favorable elastic memory properties of the polyester composition; and a chain branching agent selected from the group consisting of trifunctional alcohols and acids and tetrafunctional alcohols and acids that will copolymerize with polyethylene terephthalate, the chain branching agent being present in an amount sufficient to raise the melt viscosity of the polyester composition to a level that permits filament manufacture under conditions that are substantially the same as those under which filament can be formed from unmodified polyethylene terephthalate.

FIELD OF THE INVENTION

[0001] The present invention relates to the manufacture of yarns andfabrics and in particular relates to an improved modified polyestercomposition that is particularly useful for forming blended yarns frompolyester and cotton.

BACKGROUND OF THE INVENTION

[0002] Blended fabrics formed of polyester and cotton have found wideacceptance for fabrics, particularly for clothing. Generally speaking, a“blended” fabric of polyester and cotton is formed by spinning a blendedyarn from cotton fibers and polyester staple fibers. The blended yarnsare then woven or knitted into the appropriate fabrics. Each of thesematerials brings certain advantages and disadvantages to a fabric.Cotton is, of course, formed almost entirely of pure cellulose with atypical length of about one inch, but with variations in length fromabout a half and inch to over two inches. Mature cotton fibers arecharacterized by their convolutions so that under a microscope, cottonappears as a twisted ribbon with thickened edges. Cotton is light inweight, absorbs moisture quickly and easily, and has a generallyfavorable texture (“hand”) when woven into fabrics. Cotton lacks,however, certain strength characteristics and elastic memory, and thusgarments formed entirely of cotton require regular laundering, pressing,and in many cases starching, between wearings by the ordinary user.

[0003] Polyester is strong, light in weight, and has excellent plasticmemory characteristics. Polyester is crease-resistant, quick-drying,retains its shape in garments, is abrasion-resistant, and requiresminimum care. Because of its synthetic nature, however, polyester has agenerally unacceptable appearance (at least for most garment purposes)when initially formed as a filament. Accordingly, polyester filamentsrequire texturizing in some fashion to produce acceptablecharacteristics of appearance, hand, and comfort in yarns and fabrics.

[0004] Accordingly, blends of cotton and polyester have foundwide-ranging acceptance because of their combination of the desirablecharacteristics of cotton with those of polyester.

[0005] The characteristic advantages of polyester are such, however,that efforts continue to develop polyester filament, yarns and fabricsthat more closely resemble those of cotton, silk, rayon, or othernatural fibers. The use of polyester microfibers is one example of this,with the filaments being of such small diameter that they offerexceptionally good esthetics and hand, while retaining all of thebenefits of polyester.

[0006] A number of chemical modifications have been carried out onpolyester to attempt to obtain the desired properties, but suchtreatments can produce unwanted or unexpected characteristics in themodified polyester. For example, polyethylene glycol can enhance certainpolyester properties such as dye uptake, but can decrease otherproperties, particularly the melt phase characteristics of the polymer,that make it quite difficult to form into acceptable filaments on acontinuous commercial basis. In this regard, it will be understood thatpolyester filament is made in significantly large amounts around theworld, and that if modified polyesters are to gain commercialacceptance, they must be essentially compatible with commercialtechniques for melt-spinning, texturing, yarn spinning and fabricforming techniques; i.e., weaving and knitting.

[0007] Accordingly, a need continues to exist for enhanced polyestercompositions that have properties as close as possible to those ofcotton and other natural fibers while retaining the advantages ofpolyester.

OBJECT AND SUMMARY OF THE INVENTION

[0008] Accordingly, it is an object of the present invention to providea polyester composition that has certain properties substantiallysimilar to those of cotton, while retaining the favorable properties ofpolyester.

[0009] The invention meets this object with a polyester compositioncomprising polyethylene terephthalate, polyethylene glycol in an amountsufficient to increase the wetting and wicking properties of a filamentmade from the composition to a level substantially similar to theproperties of cotton, but less than the amount that would reduce thefavorable elastic memory properties of the polyester composition, and abranching agent in amount that raises the melt viscosity of thepolyester composition to a level that permits filament manufacture undersubstantially normal spinning conditions.

[0010] In another aspect, the invention comprises polyester filamentformed from the composition.

[0011] In yet another aspect, the invention comprises yarns formedeither entirely of polyester or of polyester and cotton blends.

[0012] In yet another aspect, the invention comprises woven, nonwoven orknitted fabrics formed from the polyester or blended yarns according tothe present invention.

[0013] The foregoing and other objects and advantages of the inventionand the manner in which the same are accomplished will become clearerbased on the following detailed description taken in conjunction withthe accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS:

[0014]FIG. 1 is a plot of the wetting characteristics of a fabric formedaccording to the present invention;

[0015]FIG. 2 is a plot of dyeing characteristics of polyester filamentaccording to the present invention; and

[0016]FIG. 3 is a plot of certain tensile characteristics for severalfilaments according to the present invention.

DETAILED DESCRIPTION

[0017] The present invention is a polyester composition that isparticularly suitable for, although not necessarily limited to,filament, yarns and fabrics. The composition comprises polyethyleneterephthalate, polyethylene glycol in an amount sufficient to increasethe wetting and wicking properties of a filament made from thecomposition to a level substantially similar to the wetting and wickingproperties of cotton or other cellulosic fibers (natural or synthetic),but less than the amount that would reduce the favorable elastic memoryproperties of the polyester composition, and a chain branching agentselected from the group consisting of tri-functional andtetra-functional alcohols and acids that will co-polymerize withpolyethylene terephthalate. The chain branching agent is present in anamount sufficient to raise the melt viscosity of the polyestercomposition to a level that permits filament manufacture underconditions that are substantially the same as those under which filamentcan be formed from unmodified polyethylene terephthalate. In preferredembodiments the polyethylene glycol is present in the polyestercomposition in an amount greater than about 4% to about 20% by weightbased on the weight of the composition, and with amounts of 6% to 16%most preferred.

[0018] The chain branching agent is preferably selected from the groupconsisting of pentaerythritol (C(CH₂OH)₄), trimesic acid (C₆H₃(COOH)₃),pyromelitic acid (C₆H₂(COOH)₄), pryomelitic dianhydride, trimeliticacid, trimelitic anhydride, and trimethylol propane (CH(CH₂₀H)₃). In themost preferred embodiments, the chain branching agent comprisespentaerythritol, but earlier work indicates that the important factorappears to be the equivalent number of branches; see, e.g. U.S. Pat.Nos. 4,092,299 and 4,113,704. The chain branching agent is present inamounts of between about 500 and 4,000 parts per million (ppm) by weightbased on the weight of the composition, and when the chain branchingagent comprises pentaerythritol, it is most preferably present inamounts of between about 1,300 and 1,800 ppm. These amounts aresufficient to provide the polyester composition of the invention with anintrinsic viscosity of between about 0.80 and 0.50 dl/g.

[0019] As used herein, the favorable plastic memory properties ofpolyester include, among others, its heat-setting characteristics(“permanent press”), and sufficient elongation to be processable underreasonable conditions. Thus, when amounts of polyethylene glycol greaterthan about 20% are present, the resulting compositions exhibit a lessuseful temperature range for processing.

[0020] As known to those familiar with the manufacture of polyester, theequipment used to spin polyester into filament is designed, built, andadjusted to handle polymers whose melt viscosity falls within a certainrange, typically between about 500 and 4000 poise. Thus, such equipmentruns most satisfactorily when the melt viscosity of the polymer (whichis directly proportional to the intrinsic viscosity in a mannerdiscussed herein), is within this range. The invention provides atechnique for including the favorable properties of polyethylene glycolinto the polyester, particularly the wetting and wicking properties thatare similar to those of cotton, but that would otherwise lower the meltviscosity of the polymer melt to a point lower than can besatisfactorily handled by normal equipment. As a result, if polyethyleneglycol alone is added in relatively significant amounts, a number ofspinning failures are likely to occur which hinder the efficiency andproductivity of the entire process.

[0021] In the present invention, however, the chain branching agentraises the melt viscosity of the polymer melt to within the range ofnormal unmodified polyethylene terephthalate, and thus within a rangethat typical equipment can handle at normally expected highproductivity. The terms melt viscosity and intrinsic viscosity are usedherein in their conventional and usual sense; i.e. melt viscosityrepresents the resistance of molten polymer to shear deformation or flowas measured at specified conditions. Melt viscosity is primarily afactor of intrinsic viscosity and temperature. In turn, intrinsicviscosity is the ratio of the specific viscosity of a polymer solutionof known concentration to the concentration of solute extrapolated tozero concentration. Intrinsic viscosity is directly proportional toaverage polymer molecular weight, see e.g., Dictionary of Fiber andTextile Technology, Hoechst Celanese Corporation (1990) and Tortora,Fairchild's Dictionary of Textiles, 7^(th) Edition (1996). Both meltviscosity and intrinsic viscosity can be measured and determined bythose of ordinary skill in this art and without undo experimentation,and indeed are widely recognized as fundamental and conventionalmeasurements of polymer characteristics. For the I.V. values givenherein, the I.V. is determined by dissolving the polymer inorthochlorophenol (“OCP”), measuring the relative viscosity (R.V.) ofthe solution using a Schott Autoviscometer (AVS Schott and AVS 500Viscosystem), and then calculating the I.V. based on the R.V. (e.g.,Dictionary of Fiber and Textile Technology, supra, at page 82). Inparticular, a 0.6 gram sample (+/−0.005g) of dried polymer sample (fiberand yarn samples are typically cut into small pieces; chip samples areground) is dissolved in about 50 ml (61.0-63.5 grams) of OCP at atemperature of about 105° C. After cooling to room temperature, thesolution is placed in the viscometer in which the relative viscosity ismeasured, and from which the intrinsic viscosity is calculated.

[0022] In another aspect, the invention comprises a polyester filament.The filament comprises polyethylene terephthalate, polyethylene glycolin an amount sufficient to increase to wetting and wicking properties ofa filament made from the composition to a level substantially similar tothe wetting and wicking properties of cotton but less that the amountthat would reduce the favorable elastic memory properties of thepolyester composition, and a branching agent, selected from the grouplisted above and most preferably pentaerythritol, in an amount thatraises the melt viscosity of the polyester composition to a level thatpermits filament manufacture under conditions that are substantially thesame as those under which filament can be formed from unmodifiedpolyethylene terephthalate. In preferred embodiments the filamentcomprises a co-polymer of the polyethylene terephthalate and thepolyethylene glycol and contains polyethylene glycol in an amount ofbetween greater than about 4% up to about 20% by weight based on theweight of the composition, with amounts of polyethylene glycol ofbetween about 6% and 16% most preferred.

[0023] As in the previous embodiment, the pentaerythritol is present inan amount of between about 500 and 4,000 ppm by weight based on theweight of the composition, with amounts of pentaerythritol of betweenabout 1,300 and 1,800 ppm being most preferred.

[0024] The polyester filament according to this embodiment of theinvention can also be cut into staple fiber which in turn can be formedinto polyester yarns using any conventional spinning technique includingring spinning, open end spinning and air jet spinning, with open end andair jet spinning becoming increasingly more preferred for polyesteryarns and blended yarns that contain polyester.

[0025] It will be understood by those familiar with textile terminologythat the term “spinning” is used to refer to two different processes. Inone sense, the term “spinning” refers to the production of syntheticpolymer filaments from a polymer melt. In its older conventional use,the term “spinning” refers to the process of twisting a plurality ofindividual fibers into yarns. The use of both of these terms iswidespread and well-understood in this art, and the particular use willbe quickly and easily recognized by those of ordinary skill in the artbased upon the context of any such use.

[0026] Accordingly, the yarns formed from the filaments of the inventioncan in turn be woven or knitted into fabrics which have the advantageouscharacteristics referred to herein.

[0027] Because of the characteristic advantages that the inventionbrings to the polyester compositions described herein, the resultingpolyester filaments are particularly useful for blended yarns thatinclude fiber according to the invention blended with another yarn, themost common of which include (but are not limited to) cotton, rayon,polypropylene and conventional polyester. Accordingly, in anotherembodiment the invention comprises a blended yarn that includes staplefibers according to the present invention. The polyester staple fiberscomprise polyethylene terephthalate, polyethylene glycol in the amountsdescribed herein sufficient to increase the wetting and wickingproperties of a filament made from the composition to a levelsubstantially similar to the wetting and wicking properties of thecotton fibers but less than the amount that would reduce the favorableelastic memory properties of the polyester staple fibers. The polyesteralso includes pentaerythritol in an amount that raises the meltviscosity of the polyester from which the staple fibers are formed to alevel that permits filament manufacture under conditions that aresubstantially the same as those under which filament can be formed fromunmodified polyethylene terephthalate.

[0028] In preferred embodiments, the polyester staple fibers comprise aco-polymer of the polyethylene terephthalate and the polyethyleneglycol. As used herein, the term copolymer refers to polymers thatinclude monomers in addition to terephthalic acid (or dimethylterephthalate) and ethylene glycol monomers. The preferred blendsinclude between about 5% and 95% by weight of the cotton fibers with theremainder comprising the polyester staple fibers. In this regard, theinvention provides the opportunity to increase the synthetic content ofblended cotton and polyester yarns in order to take increasing advantageof certain polyester's characteristics in the resulting yarns andfabrics.

[0029] As in the previous embodiments, the polyethylene glycol ispresent in the polyester staple fibers in an amount of between about 4%and 20% by weight based on the weight of the composition with amounts ofbetween about 6% and 16% most preferred. Similarly the pentaerythritolis present in the polyester staple fibers in an amount of between about1,000 and 4,000 ppm by weight based on the weight of the composition,with amounts of between about 1,300 and 1,800 ppm most preferred.

[0030] In another embodiment, the invention comprises a fabric, woven orknitted, formed from blended yarns that include fibers according to thepresent invention, and typically of cotton fibers and polyesters. Asdescribed previously, the polyester comprises polyethylene terephthalatewith polyethylene glycol present in amounts sufficient to increase thewetting and wicking properties of the fabric to a level substantiallysimilar to the properties of an entirely cotton fabric, but less than anamount that would reduce the favorable elastic memory properties of thepolyester in the fabric, with pentaerythritol in an amount that raisesthe amount viscosity of the polyester in staple fibers to a level thatpermits filament manufacturer conditions that substantially is the sameas those which filament can be formed from unmodified polyethyleneterephthalate.

[0031] As in the previous embodiments, the polyester stable fiberspreferably comprise a copolymer of polyethylene terephthalate andpolyethylene glycol, and the cotton fibers are present in the fabric inamounts of between about 5 and 95% by weight, with an amount of about30-70% by weight being preferred, and with the remainder being thepolyester.

[0032] As in the previous embodiments, the polyethylene glycol ispreferably present in the stable fibers in an amount of about 4 and 20%by weight based on the weight of the composition, and most preferablypresent in an amount of about 6 and 16%.

[0033] Similarly, pentaerythritol is preferably present in an amount ofabout 1000 and 4000 ppm by weight based on the weight of the compositionwith amounts of about 1300 and 1800 ppm being most preferred. Based onthe results to date, however, it appears that the advantages of theinvention can begin to appear at amounts of pentaerythritol of as low as500 ppm.

[0034] FIGS. 1-3 help illustrate the characteristics and advantages ofthe invention.

[0035]FIG. 1 is a plot of the area wetted in a time period of 4 minuteson a knitted hose leg by 0.5 ml of water, plotted against the percent ofpolyethylene glycol in the polyester composition. As FIG. 1demonstrates, some improvement begins when 4% of polyethylene glycol isincluded, with significant improvement appearing when the increasingamounts, (e.g., 6% and 8%) are included.

[0036]FIG. 2 is a plot of the Kubelka-Munk (K/S) reflectance value asagainst present polyethylene glycol in filaments according to thepresent invention. As known to those of ordinary skill in this art, K/Sis proportional to colorant concentration in a material. The K/S valuecan be calculated from the reflectance factor and provides an importantand generally well-understood technique for color matching. FIG. 2 plotsthe K/S value as against the percentage of polyethylene glycol inpolyester yarns formed according to the present invention at variouslevels of pentaerythritol. FIG. 2 shows K/S value for control yarns inotherwise conventional FORTREL® polyester from Wellman, Inc. FIG. 2illustrates that when pentaerythritol level is raised to the preferredamounts of 1300 or 1800 ppm, the K/S value increases significantly, thusillustrating the greatly enhanced dyeing characteristics of filamentsaccording to the present invention.

[0037]FIG. 3 demonstrates that the tensile characteristics of filamentaccording to the present invention are noticeably different from thoseof conventional polyesters, as well as different from conventionalpolyesters modified with lower amounts of polyethylene glycol. Inparticular FIG. 3 plots the TE ½ of value on a grams per denier (gpd)basis as against the draw ratio for filament formed according to thepresent invention, and shows that the results for the preferred range ofpolyethylene glycol is superior to those containing a more conventionalamount of around 2% polyethylene glycol; e.g. Blaeser et al, U.S. Pat.Nos. 4,975,233 and 5,091,504.

[0038] The information submitted illustrated in FIGS. 1-3 demonstratesthe excellent responses based on the amount of additive versus tensileproperties. Although the invention makes it possible to give a 100%match for cotton in these tensile properties, in most circumstances, itis preferable to match tenacity while leaving enough elongation for goodprocessing in fiber and yarn manufacturer. The additional amount ofpentaerythritol or other branching agent also improves the dyeingcharacteristics.

[0039] In summary, the invention provides a technique for incorporatingcotton-like characteristics into a polyester filament by modifyingpolyethylene terephthalate with copolymers to impart specificcharacteristics. The use of the branching agent produces a meltviscosity sufficient for practical processing and sufficient spinningtensions for a stable commercial process.

[0040] The degree of wetting/wicking and the level of pillingperformance can be tailored for specific applications by altering thecopolymer content of the polyester. This permits a choice of cost andbenefit in designing fabrics made with polyester or polyester/cottonblends according to the present invention. In this sense, the inventionestablishes a product technology family.

[0041] It is further expected that the amount and molecular weight ofthe polyethylene glycol can both be altered for producing specificeffects such as wetting, drying, dye rates, dye fastness, and type ofdyeing chemistry required, while improving the dye strike rate, reducingthe dye usage, and increasing the availability selection to includeionic dyes. The data reeported herein reflects the use of polyethyleneglycol with an average molecular weight of about 400 grams per mole, andpolyethylene glycols with other mole weights appear to work just aswell, at least at mole weights under 8000 g/mole as noted to date.

[0042] The invention permits the copolymers to be added to any vesselduring the process except finishing in the polymerization process.

[0043] Finally, in a fundamental sense, the use of the branching agentenhances the overall productivity of the spinning process.

[0044] In the drawings and specification, there have been disclosedtypical embodiments of the invention, and, although specific terms havebeen employed, they have been used in a generic and descriptive senseonly and not for purposes of limitation, the scope of the inventionbeing set forth in the following claims.

That which is claimed is:
 1. A polyester composition that isparticularly suitable for filament, said composition comprising:polyethylene terephthalate; polyethylene glycol in an amount sufficientto increase the wetting and wicking properties of a filament made fromthe composition to a level substantially similar to the wetting andwicking properties of cotton but less than the amount that would reducethe favorable elastic memory properties of said polyester composition;and a chain branching agent selected from the group consisting oftrifunctional alcohols and acids and tetrafunctional alcohols and acidsthat will copolymerize with polyethylene terephthalate, said chainbranching agent being present in an amount sufficient to raise the meltviscosity of said polyester composition to a level that permits filamentmanufacture under conditions that are substantially the same as thoseunder which filament can be formed from unmodified polyethyleneterephthalate.
 2. A polyester composition according to claim 1 whereinsaid chain branching agent is present in an amount that provides saidpolyester composition with an intrinsic viscosity of between about 0.5and 0.8 dl/g.
 3. A polyester composition according to claim 1 whereinsaid chain branching agent is selected from the group consisting ofpentaerythritol, trimesic acid, pyromelitic acid, pryomeliticdianhydride, trimelitic acid, trimelitic anhydride, and trimethylolpropane.
 4. A polyester composition according to claim 1 wherein saidpolyethylene glycol is present in an amount of between greater thanabout 4 percent up to about 20 percent by weight, based on the weight ofthe composition.
 5. A polyester composition according to claim 1 whereinsaid chain branching agent is present in an amount of between about 500and 4000 ppm by weight based on the weight of the composition.
 6. Apolyester composition according to claim 1 comprising a copolymer ofsaid polyethylene terephthalate and said polyethylene glycol.
 7. Apolyester filament comprising: polyethylene terephthalate; polyethyleneglycol in an amount sufficient to increase the wetting and wickingproperties of a filament made from the composition to a levelsubstantially similar to the wetting and wicking properties of cottonbut less than the amount that would reduce the favorable elastic memoryproperties of said polyester composition; and pentaerythritol in anamount that raises the melt viscosity of the polyester composition to alevel that permits filament manufacture under conditions that aresubstantially the same as those under which filament can be formed fromunmodified polyethylene terephthalate.
 8. A polyester filament accordingto claim 7 comprising a copolymer of said polyethylene terephthalate andsaid polyethylene glycol.
 9. A cut staple fiber formed from thepolyester filament of claim 7 .
 10. A polyester yarn formed from staplefibers according to claim 9 .
 11. A fabric comprising polyester yarnaccording to claim 10 .
 12. A woven fabric according to claim 11 .
 13. Aknitted fabric according to claim 11 .
 14. A nonwoven fabric accordingto claim 11 .
 15. A polyester filament according to claim 7 wherein saidpolyethylene glycol is present in an amount of between greater thanabout 4 percent up to about 20 percent by weight, based on the weight ofthe composition.
 16. A polyester filament according to claim 15 whereinsaid polyethylene glycol is present in an amount of between about 6 and16 percent.
 17. A polyester filament according to claim 7 wherein saidpentaerythritol is present in an amount of between about 500 and 4000ppm by weight based on the weight of the composition.
 18. A polyesterfilament according to claim 17 wherein said pentaerythritol is presentin an amount of between about 1300 and 1800 ppm.
 19. A blended yarncomprising: a first set of fibers selected from the group consisting ofcotton, rayon, polypropylene and conventional polyester; and polyesterstaple fibers; said polyester staple fibers comprising: polyethyleneterephthalate; polyethylene glycol in an amount sufficient to increasethe wetting and wicking properties of a filament made from thecomposition to a level substantially similar to the wetting and wickingproperties of cotton but less than the amount that would reduce thefavorable elastic memory properties of said polyester composition; andpentaerythritol in an amount that raises the melt viscosity of thepolyester composition to a level that permits filament manufacture underconditions that are substantially the same as those under which filamentcan be formed from unmodified polyethylene terephthalate.
 20. A blendedyarn according to claim 19 wherein said polyester staple fibers comprisea copolymer of said polyethylene terephthalate and said polyethyleneglycol.
 21. A blended yarn according to claim 19 wherein said first setof fibers comprise cotton fibers.
 22. A blended yarn according to claim21 wherein said cotton fibers are present in an amount of between about5 and 95 percent by weight with the remainder comprising said polyesterfibers.
 23. A blended yarn according to claim 19 wherein saidpolyethylene glycol is present in said polyester staple fibers in anamount of between greater than about 4 percent up to about 20 percent byweight, based on the weight of the composition.
 24. A blended yarnaccording to claim 23 wherein said polyethylene glycol is present in anamount of between about 6 and 16 percent.
 25. A blended yarn accordingto claim 19 wherein said pentaerythritol is present in said polyesterstaple fibers in an amount of between about 500 and 4000 ppm by weightbased on the weight of the composition.
 26. A blended yarn according toclaim 25 wherein said pentaerythritol is present in an amount of betweenabout 1300 and 1800 ppm.
 27. A blended yarn comprising: cotton fibers inan amount of between about 30 percent and 70 by weight; and polyesterstaple fibers as the remainder; said polyester staple fibers comprising:polyethylene terephthalate; polyethylene glycol in an amount sufficientto increase the wetting and wicking properties of a filament made fromthe composition to a level substantially similar to the wetting andwicking properties of cotton but less than the amount that would reducethe favorable elastic memory properties of said polyester composition;and pentaerythritol in an amount that raises the melt viscosity of thepolyester composition to a level that permits filament manufacture underconditions that are substantially the same as those under which filamentcan be formed from unmodified polyethylene terephthalate.
 28. A blendedyarn according to claim 27 wherein said polyethylene glycol is presentin said polyester staple fibers in an amount of between greater thanabout 4 percent up to about 20 percent by weight, based on the weight ofthe composition wherein said pentaerythritol is present in saidpolyester staple fibers in an amount of between about 500 and 4000 ppmby weight based on the weight of the composition.
 29. A fabriccomprising a blended yarn according to claim 28 .
 30. A woven fabricaccording to claim 29 .
 31. A knitted fabric according to claim 29 . 32.A nonwoven fabric according to claim 29 .
 33. A fabric comprising ablended yarn of: cotton fibers; and polyester staple fibers; saidpolyester staple fibers comprising polyethylene terephthalate; andpolyethylene glycol in an amount sufficient to increase the wetting andwicking properties of a filament made from the composition to a levelsubstantially similar to the properties of cotton but less than theamount that would reduce the favorable elastic memory properties of saidpolyester composition; and pentaerythritol in an amount that raises themelt viscosity of the polyester composition to a level that permitsfilament manufacture under conditions that are substantially the same asthose under which filament can be formed from unmodified polyethyleneterephthalate.
 34. A fabric according to claim 33 wherein said polyesterstaple fibers comprise a copolymer of said polyethylene terephthalateand said polyethylene glycol.
 35. A woven fabric according to claim 33 .36. A nonwoven fabric according to claim 33 .
 37. A knitted fabricaccording to claim 33 .
 38. A knitted fabric according to claim 33having the wetting properties of FIG.
 1. 39. A fabric according to claim33 wherein said cotton fibers are present in an amount of between about30 and 70 percent by weight with the remainder comprising said polyesterfibers.
 40. A fabric according to claim 33 wherein said polyethyleneglycol is present in said polyester staple fibers in an amount ofbetween greater than about 4 percent up to about 20 percent by weight,based on the weight of the composition.
 41. A fabric according to claim40 wherein said polyethylene glycol is present in an amount of betweenabout 6 and 16 percent.
 42. A fabric according to claim 34 wherein saidpentaerythritol is present in said polyester staple fibers in an amountof between about 500 and 4000 ppm by weight based on the weight of thecomposition.
 43. A fabric according to claim 42 wherein saidpentaerythritol is present in an amount of between about 1300 and 1800ppm.
 44. A polyester filament containing between about 1300 and 1800 ppmby weight of pentaerythritol and between about 4 and 8 percent by weightof polyethylene glycol and having pressure dye response propertiesdefined by one of the solid lines of FIG. 2.